1. Field of the Invention
This invention relates to an industrial robot provided with a strut supported for pivotal movement about a vertical axis, a first horizontal arm integrally mounted so as to extend sideways from the strut and pivotally moved in a horizontal plane with the pivotal movement of the strut, a second horizontal arm supported on the tip end portion of the first horizontal arm for pivotal movement in a horizontal plane, and a vertical arm supported on the tip end portion of the second horizontal arm for movement along the vertical axis and for rotation about the vertical axis.
2. Related Background Art
Heretofore, in an industrial robot comprised of a horizontal multi-articulation robot, etc., an attempt to rotate a vertical arm about a vertical axis over a range of rotation of 360.degree. or more has led to the following problem if a dog to be detected mounted on the vertical arm is only detected. That is, regarding the operation of arriving at the original point, how many times the vertical arm has been rotated is unclear and the direction of rotation of the vertical arm for arriving at the original point cannot be prescribed efficiently. Also, where the range of rotation is prescribed to a predetermined angle, it is impossible to prescribe a range of angle of 360.degree. or more with regard to overrun detection for judging whether the rotation exceeds said range of rotation. At this point, the detection width of the dog corresponding to a predetermined amount becomes necessary and therefore, exactly, a range of angle obtained by this detection width being subtracted from 360.degree. is a range of rotation within which overrun can be detected.
Therefore, heretofore, there have been known, for example, a method of providing a speed reduction mechanism in a dog, as shown in Japanese Laid-Open Utility Model Application No. 62-121091, a method of an intermittently moving portion and detecting the number of rotations, as shown in Japanese Laid-Open Utility Model Application No. 62-172594, a method of using a logic circuit by a flip-flop, as shown in Japanese Utility Model Publication No. 62-10806, and a technique of exerting contrivances on a sensor and a dog, as shown in Japanese Patent Publication No. 63-54605.
However, in such heretofore known constructions, particularly those mechanically constructed, overrun detection at an accurate position is impossible due to back-lash or the like, and the presence of mechanically contacting portions leads to problems with respect to service life and reliability reduced by abrasion.
Also, in those constructions electrically constructed, for example, regarding the arrival at the original point, even when the power source of the robot is cut off due to power failure or the like, it is necessary for a control unit to know how many times the vertical arm has been rotated, and information imparting means for backing up this becomes discretely necessary. Also, regarding overrun detection, a circuit therefor must always be kept in its operable state, and it leads to a reduction in reliability to add such an overrun detection circuit to a control circuit, and from this point of view, it is desired to the utmost that such an overrun detection circuit be not disposed between a sensor and a robot controller.